media: video-i2c: use V4L2_FRACT_COMPARE

Use V4L2_FRACT_COMPARE to check whether two v4l2_fract structs are equal.

Cc: Matt Ranostay <matt.ranostay@konsulko.com>
Cc: Sakari Ailus <sakari.ailus@linux.intel.com>
Cc: Hans Verkuil <hverkuil@xs4all.nl>
Signed-off-by: Akinobu Mita <akinobu.mita@gmail.com>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>